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Cores of Early-Type Galaxies
Published online by Cambridge University Press: 04 August 2017
Abstract
Systematic study of galaxy cores has become possible through improved understanding of seeing and the reduction of photometric errors by the use of CCDs. Many cores are well resolved in a photometry program with the Canada-France-Hawaii Telescope (median stellar FWHM = 0″.80). Core profile shape correlates with galaxy luminosity L: the brightest galaxies have isothermal profiles; fainter ellipticals and bulges have profiles that do not completely flatten inward into a core. This may be due to velocity anisotropies. Core parameters are correlated: more luminous galaxies have larger core radii and fainter central surface brightnesses. Large deviations suggest special events: Fornax A has too small and bright a core for its luminosity; it may be the remnant of a merger with a smaller galaxy. Core mass-to-light ratio M/L ∝ L0.2, as expected from the metallicity-luminosity relation. A kinematic search shows strong evidence for a central black hole in M31 and weaker evidence in M32 and NGC 3115. The nucleus of M31 rotates very rapidly but has an outer dispersion of only 107 km s−1. This implies that it is a disk; it may have formed from gas falling into the center. Rapid rotation and a central velocity dispersion > 241 ± 7 km s−1 imply a central M/Lv ≳ 20 − 35. Velocity anisotropies are not a major uncertainty because of the rapid rotation. Therefore there is strong evidence for a nuclear point mass of ~ 2 × 107M⊙.
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- Copyright © Reidel 1987
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